When transmitting conventional sterescopic television programs (so-called "3D television"), genuine sterescopic partial images are produced by means of two laterally offset cameras in the complementary colours red and green and are viewed with usual red/green anaglyphic eye glasses as a stereoscopic black-and-white image. With this known process, strong blurring and very disturbing colour spots and colour fringes occur in out-of-focus image areas. Only a black and white image impression is obtained. The observer rapidly becomes tired, particularly with moving scenes. Thus, an observer often would prefer to see the program without anaglyphic eye glasses; that, however, is only possible with a strong loss of image quality because only a very unsharp image impression is possible without anaglyphic eye glasses.
With all genuine stereoscopic processes, the expense for the production of the programs is considerable. Already available monoscopic records can be observed only as such.
In another known process of displaying television images which is applicable also to already available monoscopic pictures (U.S. Pat. No. 4,264,926), the aim is to utilize a disparity between two monoscopic pictures taken at different times for obtaining the impression of a three-dimensional image.
However, the storing of the past image in a colour television receiver requires a very high expense. The result is unsatisfactory because the desired success can be obtained only if the moving elements of the scene move at a definite speed in a definite horizontal direction (with a normal attitude of the head of the observer).
Furthermore, is has been known for quite a time that a three-dimensional image impression can be obtained also with partial image which are derived from the same monoscopic image. That principle has been described not only for purely optical devices (Belgian patent letter No. 535 959) but also for television receivers. According to the U.S. Pat. No. 4,151,549, a projection colour television receiver is employed which comprises three projectors, one each for three basic colours. Means (not decribed in detail) are provided to selectively offset one of the produced projected partial images with respect to the other partial image. The mutually offset partial images are separately viewed through polarization filters. That process is very expensive and not suited for the vast majority of receiving apparatuses which operate without means for projection, or with a single projector only.
A known process of the kind initially set forth (German Auslegeschrift No. 1 164 467) operates in a similar manner In that process, two beam generating systems of a two beam picture tube, which systems write in complementary colours, are controlled with one and the same black and white image signal, and the partial images produced by the two beams are mutually laterally offset by means of a control device which has not been described in detail. That proposal did not find acceptance in practice, presumably for the reason that the mutual offsetting of the partial images involved difficulties. The present invention proceeds from that part of the known process. The known process, however, still employs additionally a non-linear contrary distortion of the time deflections of the two beams in order to make the two partial images perspectively different and to thus amplify the impression of a three-dimensional image. However, since the additional stereoscopic effect thus created can at best be randomly now and then be in accordance with the actual perspective of the image scene, a satisfactory impression of a three-dimensional picture cannot result in this manner. However, that additional feature reflects the belief that in view of the unsatisfactory effectiveness of the genuine stereoscopic television processes mentioned initially, it had to be considered a devious idea to simply employ a pseudo-stereoscopic process from which a further reduction of the standard had to be fairly expected.